An oil sand usually consists of a mixture of clay substance, silicates, water and hydrocarbons. The oil phase contained up to 18% in oil sands consisting of various hydrocarbons has a very different composition, often specific to the extraction area, wherein bitumen, crude oil and asphalt can be contained therein. The processing of oil sand is carried out with the aim of separating the stone or sand fraction comprising clay substance and silicates from the actual valuable material, i.e. the oil phase comprising the hydrocarbons.
Oil sands are frequently extracted in open cast workings. For extraction from deeper layers of the earth preprocessing is often undertaken, in which the steam is introduced into the deposits, the hydrocarbons are liquefied and collected at drilling rigs and bought to the surface.
U.S. Pat. No. 4,240,897 describes a method for extraction of bitumen from oil sand by means of hot water.
DE 10 2007 039 453 A1 describes a method for obtaining bitumen from oil sand-water mixtures by means of flotation.
According to the CLARK-ROWE process, oil sand is mixed with sodium hydroxide and hot water and the oil phase is mobilized thereby. A water-oil phase separation is primarily undertaken by flotation. The remaining stone or sand component still contains up to 20% of the oil phase after the extraction, which in part is bound adsorptively to the surface of the finest particles. This leads to a steric stabilization of these particles in the waste water flow of the process, making separation of these particles very much more difficult. Furthermore a significant amount of clay substance is so greatly hydrophobized by an adsorptive agglomeration of the oil phase so that this gets into the product during a flotation, i.e. the separated oil phase. The clay substance represents a quality reducing contamination there, which can only be separated again with difficulty. Depending on oil sand composition, to obtain a barrel of oil phase around two to five times the amount of non-recyclable fresh water is needed. The water is stored temporarily or finally in collection basins with the separated stone or sand fraction.
U.S. Pat. No. 4,968,412 describes a two-stage method for removal of bitumen from oil sand, in which in a first step organic solvents are supplied and the clay substance is separated. In a second step the processed oil sand is washed with water while adding surfactants.
U.S. Pat. No. 3,542,666 describes a method for extraction of hydrocarbons from oil sand, in which organic solvents in combination with a small amount of water are mixed in specific quantity ratios with the oil sand to a suspension and the pH value of the suspension is set to at least 5 before there is filtration of the suspension.
The unpublished European patent application with the file reference EP 10156735 describes a method for extraction of hydrocarbons from oil sand. It has been shown that a use of purely organic extraction means leads to the finest components which predominantly consist of clay substance agglomerating in the oil sand and the agglomerates additionally exhibiting a hydrophobic behavior. This makes possible a separation of the clay substance with the stone and sand fraction by means of a mechanical solid-liquid filtration. In this process the oil sand is suspended with organic solvents and filtered by means of a continuous filter, especially a drum filter. The filter cake formed is washed in a filter unit by means of at least one first wash liquid and subsequently steamed with a steam formed from a second wash liquid, wherein residues still present in the filter cake of the first wash liquid(s), including possible hydrocarbon residues, are driven out of the oil sand. The filter cake is cleaned and largely dehumidified in this case. In this case the application of the first wash liquid(s) to the filter cake can be undertaken by means of a dispensing device, which e.g. is realized by nozzles.
The driving out of the residual amount of first wash liquid from the filter cake is also referred to in the literature as steam pressure filtration.
The basics of steam pressure filtration are known and are described for example in the following publications:
“Steam Pressure Filtration: Mechanical-Thermal Dewatering Process”, U. A. Peuker, W. Stahl, Drying Technology, 19(5), pages 807-848 (2001);
“Applying mechanical-thermal filtration processes for purification, e.g. solvent removal”, U. A. Peuker, Proc. Filtech Europe, 12.-23. Oct. 2003, Düsseldorf, Germany;
“Abtrennung von organischen Lösemitteln aus Filterkuchen mit Dampf” (Separation of organic solvents from filter cakes with steam), U. A. Peuker, F & S Filtrieren and Separieren, Volume (2003), No. 5, pages 230 to 236;
“Steam Pressure Filtration for the treatment of limey soils contaminated with aliphatic hydrocarbons”, by M. Bottlinger, H. B. Bradl, A. Krupp, U. Peuker, 2nd Int. Containment & Remediation Technology Conference, 10-13 Jun. 2001, Orlando, Fla., USA;
The filter cake, comprising the stone or sand fraction of the oil sand, is freed from first wash liquid when the steam is pushed through it and at the same time a quantity of hydrocarbons or oil phase dissolved therein is driven out. This increases the yields of hydrocarbons or improves the separation degree to around 95 to 98%, which characterizes the separation success.
U.S. Pat. No. 3,969,247 and EP 0 326 939 A2 disclose a filtration process using a drum filter in which the water vapor is pushed through the filter cake produced.
It has been shown that with some suspensions to be filtered a filter cake is formed with a surface layer which differs in its composition from the rest of the filter cake and makes washing and steaming of the filter cake more difficult. In the case of suspensions of oil sand and organic solvents this situation occurs for example when there is a high bitumen content in the suspension. It forms a surface layer thickening the filter cake towards the top containing a high proportion of asphalt clay substance agglomerates, which make it difficult or impossible for the wash liquid to flow through the filter cake. On occurrence of such compositions of the suspension to be filtered the yield of hydrocarbons from the oil sand is thus markedly reduced.
Filter devices are already known from U.S. Pat. No. 1,963,616, U.S. Pat. No. 4,521,314 and German publication No. 2106131 in which the surface of the filter cake formed is peeled off and the peeled-off material is fed back into the suspension and dissolved again therein.